One Antenna is a coupling element or a conductive system interchanging electromagnetic energy of the circuit. When transmitting the signal, the electricity of the radio frequency is transferred by the antenna to the electromagnetic energy and is radiated to the surroundings. When receiving the signal, the electromagnetic energy received by the antenna is transferred to the electricity of the radio frequency which is provided and accessed to the processor. Generally speaking, the characteristic and the efficiency of the antenna are obtained from the parameters, such as operation frequency, radiation pattern, return loss, and antenna gain, etc., wherein the radiation pattern resulting from the antenna radiate energy in all directions is the characteristic of the antenna radiation described as the space function by the figure.
Due to the different communication products have different restriction or function, the antenna design for radiant or received signals have diversities, such as dipole antenna, monopole antenna, traveling-wave wire antenna, helical antenna, spiral antenna, ring antenna, microstrip antenna, and print antenna, etc. In the wireless network application, the products having excellent covering range on the horizontal plane are needed, so the dipole antenna is generally used to obtain the omnidirectional radiation pattern. However, the drawbacks of the dipole antenna lies in that the dipole antenna is protruded from the product and the product volume and the difficulty of the design are increased. The microstrip antenna has the advantages of small volume, light weight, low cost and easy production. Therefore, for further minimizing the product volume, the microstrip antenna is an adoptable means.
The current microstrip antenna includes many feeding methods, such as coaxial cable feed, microstrip feed, and coplanar waveguide (CPW) feed, etc., wherein the method of using coaxial cable feed is more common. Please refer to FIG. 1, which is a structural diagram showing a coaxial cable fed (ring-shaped) microstrip antenna according to the prior art. In FIG. 1, a microstrip antenna 10 includes a plane-shaped dielectric substrate 101, a radiant metal sheet 102, a metal ground plane 105, and a coaxial cable 103. The radiant metal sheet 102 is disposed on one side of the dielectric substrate 101, and the metal ground plane 105 is stuck on another side of the dielectric substrate 101. The coaxial cable 103 passes through the metal ground plane 105 and is connected to radiant metal sheet 102. When receiving the signal, the electromagnetic energy radiation received by the radiant metal sheet 102 is transferred to a current of the radio frequency transmitted and accessed to the receptor by the coaxial cable 103. In the same way, when transmitting the signal, the current signal of the radio frequency transmitted from the coaxial cable 103 is transferred by the radiant metal sheet 102 to the electromagnetic energy radiation. The drawback of the microstrip antenna fed into the coaxial cable is the narrow bandwidth, and it is generally used in the mobile phone with the narrower bandwidth demand, such as GSM system. However, the bandwidth is about 3% in the 2.4 GHz application, which is insufficient to provide enough bandwidth in the standard of 802.11b/g in the presently mainstreamed wireless network.
In order to increase the effective bandwidth of the microstrip antenna, another current feed method is achieved by using aperture couple. Please refer to FIG. 2, which is a structural diagram showing an aperture coupled microstrip antenna according to the prior art. In FIG. 2, the aperture coupled microstrip antenna 20 includes two substrates 2011 and 2012, a radiant metal sheet 202 with a spectacular shape stuck on one side of the first substrate 2011, and a metal ground plane 205 stuck on one side of the second substrate 2012 arranged near to the first substrate 2011. The metal ground metal 205 includes an aperture 203 exposing the second substrate 2012, and a metal feed line 204 exposing on another side of the second substrate 2012 which received and transmitted the current signal with a specific frequency through the aperture 203. The bandwidth is increased about 6% by using microstrip antenna coupled with an aperture, but the present ring antennas in general all are the fundamental mode of the excited antenna. Moreover, the radiation pattern of the ring antenna is provided as a single direction in the fundamental mode and restricted in the application. At the same time, it remains to be insufficient for the progressive wireless surroundings.
It is therefore attempted by the applicant to deal with the above situation encountered in the prior art.